#back{
  width: 100%;
  min-height: 100vh;
  background-color: #efccff;
  background-image: 
    radial-gradient(closest-side, #19b6ff,rgba(0,0,0,0)),
    radial-gradient(closest-side, #ff9999,rgba(0,0,0,0)),
    radial-gradient(closest-side, #f07b3f,rgba(0,0,0,0)),
    radial-gradient(closest-side, #d59bf6,rgba(0,0,0,0)),
    radial-gradient(closest-side, #ffb400,rgba(0,0,0,0));
  background-size: 
    130vmax 130vmax,
    80vmax 80vmax,
    90vmax 90vmax,
    120vmax 120vmax,
    90vmax 90vmax;
  background-position: 
    -80vmax -80vmax,
    60vmax -30vmax,
    -30vmax -10vmax,
    20vmax 80vmax,
    10vmax 10vmax;
  background-repeat: no-repeat;
  position: fixed;
  z-index: -1;
  animation: 10s movement linear infinite;
  backdrop-filter: blur(10px);
}
#back::after{
  content: '';
  display: block;
  position: fixed;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  // backdrop-filter: blur(10px);
  // -webkit-backdrop-filter: blur(10px);
}
@keyframes movement{
  0%{
    background-size: 
      130vmax 130vmax,
      80vmax 80vmax,
      90vmax 90vmax,
      120vmax 120vmax,
      90vmax 90vmax;
    background-position: 
      -80vmax -80vmax,
      60vmax -30vmax,
      -30vmax -10vmax,
      20vmax 80vmax,
      10vmax 10vmax;
  }
  25%{
    background-size: 
      110vmax 110vmax,
      90vmax 90vmax,
      100vmax 100vmax,
      90vmax 90vmax,
      60vmax 60vmax;
    background-position: 
      -60vmax -90vmax,
      50vmax -40vmax,
      0vmax -20vmax,
      -20vmax 50vmax,
      40vmax 60vmax;
  }
  75%{
    background-size: 
      90vmax 90vmax,
      90vmax 90vmax,
      100vmax 100vmax,
      90vmax 90vmax,
      70vmax 70vmax;
    background-position: 
      -50vmax -40vmax,
      50vmax -30vmax,
      20vmax 0vmax,
      -10vmax 10vmax,
      40vmax 60vmax;
  }
  100%{
    background-size: 
      130vmax 130vmax,
      80vmax 80vmax,
      90vmax 90vmax,
      120vmax 120vmax,
      90vmax 90vmax;
    background-position: 
      -80vmax -80vmax,
      60vmax -30vmax,
      -30vmax -10vmax,
      20vmax 80vmax,
      10vmax 10vmax;
  }
}